1. Prior Art
Organosolv hydrolysis processes have been successfully demonstrated on certain types of cellulosic materials particularly lignocellulosics. The easiest wood to delignify by organosolv solutions is aspen while conifers such as hemlock, Douglas-fir and pines showed substantial resistance. Sugarcane rind was found to be relatively easy to hydrolyze. Cotton linters which are essentially cellulose, especially the crystalline fraction, were very difficult to hydrolyze by prior art processes. The reasons for the hydrolysis differences are related to variations and heterogeneity in structure and the chemical composition of cellulosic materials. Thus traditionally organosolv processes have been used primarily with cellulosic materials which are easy to delignify. Cotton linters have been avoided especially in saccharification work because of their resistance to hydrolysis and the harsher process conditions required for their hydrolysis in rapid conversion of the polymeric glucan to monomeric sugars.
The prior art has described various organosolv processes for delignification and/or saccharification of cellulosic materials and vegetable crops. In general such processes involve the use of a mixture of water and a solvent such as alcohols or ketones and sometimes other solvents of a non-polar nature along with an acidic compound to facilitate the hydrolysis. In most instances there is a several hour treatment required to accomplish delignification and additional hydrolysis of the cellulosic residue, depending on the hydrolysis power of the solvent system used and its ability to delignify the particular lignocellulosic material. Prior art processes have been characterized by poor delignification ability, slow hydrolysis rates and extensive sugar conversion into non-sugars, mainly furfurals and organic acids. Hence the sugar recoveries were too low to be commercially attractive to develop such processes on a commercial scale. All of the prior art sacharification processes, of which we are aware of, suffer to some degree from one or the other of these disadvantages. It has long been thought that such were inherent in organosolv processes, particularly with difficult to hydrolyse cellulosic materials such as cotton linters and the conifers.
Thus U.S. Pat. No. 1,919,623 to Dreyfus (1933) describes pretreatment of wood with concentrated acid in acetone-water carrier solvent mixtures and after removal of the organic solvent heating the caid-containing wood at low temperature for several hours to cause in situ hydrolysis of the carbohydrates without simultaneous dissolution of the lignin. The treated lignocellulose was reportedly practically insoluble in the acetone-ether water mixtures, on treatment of the prehydrolysed material with the same solvent only the excess acid was removed and used in further treatments. Decomposition of the pre-hydrolysed cellulose material to sugars was effected on boiling in an aqueous weak acid solution. U.S. Pat. No. 2,022,654 also issued to Dreyfus describes a similar approach for the production of cellulose pulp in that wood chips are pre-treated with concentrated mineral acid carried in up to 80% acetone in water to soften the wood and after substantially removing all the acid the chips are treated for 9 to 12 hours at 170.degree. C. to 230.degree. C. in a pressure vessel using 50 to 80% acetone water or mixtures of acetone and non-polar organic solvent. U.S. Pat. No. 2,959,500 to Schl/a/ pfer et al describes a hydrolysis process with the solvent consisting of alcohols and water and optionally of a non-polar solvent at 120.degree. C. to 200.degree. C. in the presence of a small amount of an acidic compound which was claimed by the inventors as unreactive with the alcohols. The process as thought is relatively slow and limited in saccharification power and the sugar yields are much less than quantitative. U.S. Pat. No. 1,964,646 to Oxley et al (1934) shows slow saccharification with strong acid. U.S. Pat. No. 1,856,567 to Kleinert and Tayenthal (1932) teaches the use of aqueous alcohol at elevated temperatures for production of cellulosic pulp in a pressure vessel using small quantities of caids or bases as delignification aids. The treatment is described in steps of three hours each. Other prior art is described in U.S. Pat. No. 2,951,775 to Apel in which wood is saccharified by the use of multiple applications of concentrated hydrochloric acid at 25.degree. C. to 30.degree. C.
2. Objects of Invention
The main object of the present invention is to rapidly and quantitatively solubilize and recover chemical components of cellulosic materials.
A further object of the invention is to reduce the hydrolysis time and substantially increase sugar formation rates in hydrolysing cellulosic materials.
A further object of the invention is to reduce sugar degradation to non-sugars during high temperature hydrolysis of cellulosic materials.
A further object of the invention is to simultaneously dissolve and then recover separately the chemical constituents of cellulosic materials to yeild mainly xylose, hexose sugars and lignin if the material is lignocellulosic.
A further object of of the invention is to, if so desired, convert the isollated pentoses and hexoses into respective dehydration products such as furfural and hydroxymethyl furfural, levulinic acid by re-exposure to high temperature and recover monomeric furfurals, levulinic acid.
A further object of the invention is to quantitatively hydrolyse cellulosic materials at such a rate that, when the organic volatiles are evaporated from the hydrolysis liquor and the lignin if any is separated from the aqueous solution, higher than 10 percent by weight sugar solids is obtainable from the solution.
A further object of the invention is to substantially reduce the concentration of acid required to maintain and regulate a given hydrolysis rate and thereby substantially reduce the catalytic effects of acids in degradation of sugars at high temperature.
Alternately, the object of the present invention is to reduce the reaction temperature required to achieve a certain desirable reaction rate during the hydrolysis process and thereby maximize the sugar recovery.
A further object of the present invention is to reduce the energy required for hydrolysis by use of a major volume proportion or in excess of 70 percent of acetone which has heat capacity and heat of vaporization much lower than that of water and thus can be easily volatilized to cool the hydrolysis liquor.
A further object of the invention is to obtain substantially pure low DP cellulose on very short selective delignification and hydrolysis of cellulosic materials, which is useful as animal fodder, food additive and as industrial filler and adsorbent.
These and other objects will become increasingly apparent by reference to the following description.